This invention relates generally to kinescopes for television receivers and particularly to a drive level control system for use in testing such tubes.
The precise control of the video drive level of a kinescope is required during the visual testing which takes place after the final steps of the manufacturing process are completed. During such testing the completed kinescopes are mounted in a test fixture which is used to apply the video drive voltage to the kinescope. In order to assure that every kinescope is tested under substantially identical conditions, it is necessary to precisely control the video drive level of the test set. In the absence of precise control of the test conditions, the results can indiscriminately vary and lose significance. This is particularly true because the tests, typically are subjective visual tests which, are performed by the human eye. For example, one of the tests is the ability of the tube to properly focus. In this test, a pattern, such as a grid, is placed on the screen. A tube which properly focuses the electron beams will create sharp, fine lines in the grid pattern. However, variations in the video drive level can cause the electron beams to spread on the screen and the grid lines in the corners will spread, or flair. Thus, an acceptable tube can be improperly rejected because of of a variation in the test voltage.
The instant invention overcomes these difficulties by the provision of a system which automatically maintains a uniform video drive level on the electron gun of a kinescope.